1. Field of the Invention
The present invention relates to a lens driving apparatus and an image pickup apparatus including the lens driving apparatus. More specifically, the present invention relates to a lens driving apparatus and an image pickup apparatus allowing free focus adjustment and camera shake correction.
2. Description of the Background Art
Conventionally, it has been known that when a DC electric field is applied to a crystalline body, a strain is generated in the crystalline body. A crystalline body in which strain generates upon application of the DC electric field is referred to as an electrostrictive element.
The electrostrictive element is classified into those producing electrostrictive effect, in which strain of one same direction is generated regardless of the direction of electric field generated in the crystalline body, and those producing piezoelectric effect in which direction of strain generation differs dependent on the direction of electric field generated in the crystalline body. Generally, the electrostrictive effect is produced in a crystalline body having a symmetrical crystal structure and the piezoelectric effect is produced in a crystalline body having an asymmetrical crystal structure.
An actuator realizing mechanical operation through the use of such an electrostrictive element has been proposed. By way of example, Japanese Patent Laying-Open No. 06-216424 discloses a deformation actuator utilizing a piezoelectric element, which is an electrostrictive element producing the piezoelectric effect, having a strip-shaped piezoelectric element spirally wound on a surface of a hollow coil spring. By such a deformation actuator, a small amount of strain (amount of displacement) of the piezoelectric element is enlarged to attain a sufficient amount of displacement to attain the function of the actuator.
The deformation actuator disclosed in Japanese Patent Laying-Open No. 06-216424 mentioned above, however, requires a complicated process step of spirally winding the strip-shaped piezoelectric element on the surface of the hollow coil spring. In this connection, International Publication No. WO2002/103451 discloses a camera in which an electrically active substance formed to have a spiral shape drives a lens. In this camera, the spiral-shaped electrically active substance functions as an actuator.
In the camera disclosed in International Publication No. WO2002/103451, positioning of a camera lens means focusing and zooming operations of the camera, and the lens moves along an optical axis only.
Therefore, inclination of a lens with respect to the optical axis caused in the process of assembly, or blurring due to hand movement (camera shake) at the time of image pickup cannot be corrected. Further, as the lens is held by one coil (actuator), shock-tolerance is unsatisfactory.